Suppression of deep-level traps via semicarbazide hydrochloride additives for high-performance tin-based perovskite solar cells

Abstract Tin perovskites with exemplary optoelectronic properties offer potential application in lead-free perovskite solar cells. However, Sn vacancies and undercoordinated Sn ions on the tin perovskite surfaces can create deep-level traps, leading to non-radiative recombination and absorption of nucleophilic O2 molecules, impeding further device efficiency and stability. Here, in this study, a new additive of semicarbazide hydrochloride (SEM-HCl) with a N–C=O functional group was introduced into the perovskite precursor to fabricate high-quality films with a low concentration of deep-level trap densities. This, in turn, serves to prevent undesirable interaction between photogenerated carriers and adsorbed oxygen molecules in the device’s operational environment, ultimately reducing the proliferation of superoxide entities. As the result, the SEM-HCl-derived devices show a peak efficiency of 10.9% with improved device stability. These unencapsulated devices maintain almost 100% of their initial efficiencies after working for 100 h under continuous AM1.5 illumination conditions. Graphical Abstract Supplementary Information The online version contains supplementary material available at 10.1007/s12200-023-00103-1.

MoO3 and Al were purchased from Ji'lin OLED Co., Ltd and Zhong Nuo Advanced Material (Beijing) Technology Co., Ltd, respectively.All these materials were used as received without further treatment.
Indium tin oxide (ITO) deposited glass substrate was cleaned in deionized (DI) water, acetone, and ethanol subsequently and respectively for 20 min in an ultrasonicator (Shumei KQ300DE).After dried with nitrogen gas, the ITO surface was treated with UV-ozone using an ODT UV-O3 Cleaner for 15 min.Then, PEDOT:PSS was spin-coated on ITO at 4000 rpm for 60 s in air, followed by annealing at 120 o C for 20 min.The PEDOT:PSS-coated ITO was then transferred into a glove box filled with high-purity N2.The Sn perovskite precursor was prepared by mixing FAI, MAI, SnI2 and SnF2 at a molar ratio of 0.75:0.25:1:0.1 with a concentration of 1.0 mol/L in the mixed solvent of DMF/DMSO (4/1, v/v) and stirring at 25 o C for 2 h.For the SEM-HClderived precursor solution, the molar ratio of SEM-HCl and SnI2 was 3%.Then perovskite precursor was spin-coated on the surface of ITO/PEDOT: PSS substrates at 5000 rpm for 30 s, then 150 µL of chlorobenzene was quickly dropped on the center of the substrates at the 13th s of the spin-coating process to produce the dense perovskite crystal film followed by 70 o C thermal annealing for 10 min.Finally, the C60 (20 nm), BCP (6 nm) and Al (100 nm) layers were sequentially evaporated on the surface of perovskite films.The thickness was precisely controlled by crystal oscillator during the vapor deposition process.The area of the Al electrode was determined by a mask and the active area of a single device is 0.09 cm 2 .

Characterization
The fabricated devices were measured without encapsulation at room temperature perturbation was applied at different direct current voltages ranging from 0 to 0.5 V with frequencies between 105 and 1 Hz under dark conditions.The results were fitted using the software of Zsim.All characterizations and measurements were performed in ambient conditions.

(
25 o C) in N2 atmosphere.Their photocurrent density-voltage (J-V) curves and power conversion efficiencies (PCEs) were obtained by a computer-programmed Keithley 2400 source/meter under 100 mW/cm 2 illumination of AM 1.5G solar simulator (SAN-EI Electric Co., Ltd.).The external quantum efficiency (EQE) measurements were conducted in air by QE-R system (Enli Technology Co., Ltd.).The SCLC characterization was performed on hole-only devices with the structure of ITO/PEDOT: PSS (~ 40 nm)/perovskite (130~160 nm)/MoO3 (10 nm)/Al (100 nm), all devices were measured from 0 to 7 V with a step size of 0.02 V under dark conditions using the J-V sweep mode developed by a Keithley 2400 source/meter unit.UV-vis absorption spectra were obtained on a Jasco V-750 UV-Visible/Near-Infrared Spectrophotometers.The Fourier Infrared spectra were characterized by PE-Spectrum Two in transmittance model.X−ray diffraction (XRD) and scanning electron microscopy (SEM) characterizations of FA0.75MA0.25SnI3films were conducted on Rigaku Smart lab X-Ray diffractometer and Hitachi S-4800 scan electron microscope, respectively.Steady-state photoluminescence (PL) spectra were collected using Hitachi F-4600 spectrofluorometer (Japan).The time-resolved PL decays of the perovskite films were measured by an Edinburgh FLS 980.A 450 nm pulse laser with a repetition frequency of ~1-20 MHz was employed to measure the PL lifetime by a fitted biexponential decay model (I=I1×exp[−(t/τ1)]+I2×exp[−(t/τ2)]).X-ray photoelectron spectroscopy (XPS) experiments were carried out on an ESCALAB 250 system equipped with a monochromatic Al Kα X-ray source (hv=1486.6eV).The atom force microscopy (AFM) measurements were performed at room temperature using Bruker Dimension Icon AFM equipped with Scanasyst-Air peak force tapping mode AFM tips from Bruker.The electrochemical impedance spectra (EIS) were measured on a CHI660 electrochemical workstation (CH Instrument Inc.).A 20 mV voltage

Fig. S1 .
Fig. S1.Top-view SEM images of the perovskite films at low magnifications.

Fig. S2 .
Fig. S2.Time-resolved PL decay profiles of the control and SEM-HCl-derived perovskite films.

Figure S5 .
Figure S5.Energy Level diagram of the SEM-HCl derived TPSCs.

Figure S6 .
Figure S6.Device performance statistics on (a) Voc, (b) FF and (c) Jsc of the control and SEM-HCl derived TPSCs.

Fig. S7 .
Fig. S7.Nyquist plots of the EIS measurements of control and SEM-HCl-derived TPSCs under dark condition.